Rubbing between the central rotor and the surrounding stationary components of
machinery such as large-scale turbine units can escalate into severe vibration,
resulting in costly damage. Although conventional vibration analysis remains an
important condition monitoring technique for diagnosing such rubbing phenomena,
the non-destructive measurement of acoustic emission (AE) activity at the
bearings on such plant is evolving into a viable complementary detection
approach, especially adept at indicating the early stages of shaft-seal rubbing.
This paper presents a case study on the application of high-frequency acoustic
emissions as a means of detecting and verifying shaft-seal rubbing on a 217 MVA
operational steam turbine unit. The generation of AE activity is attributed to
the contact, deformation, adhesion and ploughing of surface asperities on the
rubbing surfaces of the rotor and stator.